1. Field of the Invention
The present invention relates to a light-emitting apparatus having a semiconductor light-emitting device. In particular, the invention relates to a semiconductor light-emitting apparatus in which a semiconductor light-emitting device, or excitation light source, and a wavelength conversion portion are combined to chiefly emit white light.
2. Description of the Related Art
FIG. 1 shows a known light-emitting apparatus that uses a wavelength conversion material. This light-emitting apparatus can include an insulating base 10, a semiconductor light-emitting device 12, and a light transmitting substrate 16 which is arranged on the insulating base 10. A pair of lead electrodes 11 can be formed on the surface of a substrate under the insulating base 10. The insulating base 10 can also have a concave portion 13 and a curved portion 14. The semiconductor light-emitting device 12 can be placed at the center of the bottom of the concave portion 13. The curved portion 14 can be continuous to the periphery of the concave portion 13. The semiconductor light-emitting device 12 placed at the center of the bottom of the concave portion 13 can be electrically connected with the pair of lead electrodes 11. A wavelength conversion layer 15 can be formed on a surface of the light transmitting substrate 16 where it faces the base 10.
For the sake of efficient light reflection, a reflecting film 17 made of Ag or the like can be formed on the inside of the concave portion 13 and the surface of the curved portion 14. The wavelength conversion layer 15 can be made of a resin in which phosphor materials are dispersed. The phosphor materials can be configured/selected for emitting light when excited by excitation light emitted from the semiconductor light-emitting device 12. The wavelength conversion layer 15 can be formed on the light transmitting substrate 16 by such means as screen printing. The light transmitting substrate 16 can be placed so that the wavelength conversion layer 15 is opposed to the semiconductor light-emitting device 12 and can be situated substantially directly above the concave portion 13 accommodating the device 12. The base 10 having the concave portion 13 and the curved portion 14 can, in conjunction with the light transmitting substrate 16 provided with the wavelength conversion layer 15, define a space which is filled with a translucent sealing material 18 to seal the semiconductor light-emitting device 12 and the wavelength conversion layer 15. Incidentally, the reflecting film 17 on the curved portion 14 may be coated with a second wavelength conversion layer 19 (for example, see Japanese Unexamined Patent Application Publication No. 2004-56075 A or its corresponding U.S. Pat. No. 6,809,342).
In the light-emitting apparatus described above, the concave portion 13 for accommodating the semiconductor light-emitting device and the curved portion 14 can and often should be formed for the sake of improved light emission efficiency. Suppose, for example, the light-emitting apparatus of this configuration is applied in a white chip LED (a surface mountable LED device emitting light in the white wavelength range) or the like for use in a liquid crystal display backlight of a cellular phone or mobile information terminal. The mold for forming the base 10 having the concave portion 13 and the curved portion 14 can and often should have a high degree of precision, and thus may require extremely high skill for fabrication. As a result, there have been problems relating to increased costs for the white chip LED, difficulty in manufacturing, etc.
With an extremely simple configuration in which the first wavelength conversion layer 15 is formed alone without the curved portion 14 or the second wavelength conversion layer 19, the light-emitting apparatus can develop unevenness in color inside. A reason for this is as follows: When the light-emitting apparatus is viewed from its optical axis, the color of the excitation light is dominant in an area immediately near the semiconductor light-emitting device 12. Meanwhile, the color complementary to that of the excitation light, occurring from the wavelength conversion layer, is dominant in surrounding areas somewhat away from the area immediately near the semiconductor light-emitting device 12. In terms of intensity (intensity distribution), there have been problems in that the intensity peaks at the area immediately near the semiconductor light-emitting device 12 and it decreases toward the periphery.
Next, we will analyze the case where the base 10 is provided with the concave portion 13 alone without the curved portion 14, and only the second wavelength conversion layer 19 is formed on the inside of the concave portion 13 without the first wavelength conversion layer 15. Here, when the light-emitting apparatus is viewed from its optical axis, the light of the semiconductor light-emitting device 12 has difficulty in reaching the second wavelength conversion layer 19. Consequently, the complementary color of the excitation light, i.e., the light from the wavelength conversion layer 19 is dominant in the area immediately near the wavelength conversion layer 19 while the color of the light emitted from the semiconductor light-emitting device 12 is dominant in the other areas. That is, unevenness in color has also occurred in this case. As for intensity distribution, there have also been problems similar to the intensity problems described above.